/* Copyright (C) 2013-2021 TU Dortmund
 * This file is part of AutomataLib, http://www.automatalib.net/.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package net.automatalib.graphs.concepts;

import org.checkerframework.checker.nullness.qual.Nullable;

/**
 * Initial node concept. Graphs implementing this interface expose a designated initial node.
 *
 * @param <N>
 *         node class.
 *
 * @author Malte Isberner
 */
public interface InitialNode<N> {

    /**
     * Retrieves the initial node, or {@code null} if this graph does not have an initial node.
     *
     * @return the initial node.
     */
    @Nullable N getInitialNode();
}
